View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Springer - Publisher Connector Corinthian Bronze and the Gold of the Alchemists DavidM Jacobson The Centre fOr RapidDesign and Manufacture, Buckingham Chilterns University College, High Wycombe, HP11 2JZ, UK Received: 1 July 1999 Alloys that went under the name of Corinthian Bronze were highly prized in the Roman Empire at the beginning of the Christian era, when Corinthian Bronze was used to embellish the great gate of Herod's Temple in Jerusalem. From the ancient texts it emerges that Corinthian Bronze was the name given to a family of copper alloys with gold and silver which were depletion gilded to give them a golden or silver lustre. An important centre of production appears to have been Egypt where, by tradition, alchemy had its origins. From an analysis of the earliest alchemical texts, it is suggested that the concept of transmutation of base metals into gold arose from the depletion gilding process. CORINTHIAN BRONZE AND ITS main constituent because it is classified as bronze (aes IDENTIFICATION in Latin), and is discussed by Pliny in the section of his encyclopaedia dealing with copper and bronze. Ancient texts in Latin, Greek, Hebrew and Syriac refer However, Pliny indicates that their hue varied from to a type of metal called Corinthian Bronze which they golden to silvery, depending on the proportions of the prize above all other copper alloys. The Roman precious metal additions, and it was this lustre that encyclopaedist, Pliny, who lived in the 1st century AD, gave this bronze its attractive appearance. Both Cicero states that Corinthian Bronze was valued "before silver and Plutarch comment on the fact that, unlike other and almost before gold" (1). He proceeds to discuss the copper alloys, Corinthian Bronze was resistant to appearance and composition of Corinthian Bronze as tarnishing (6). Tagged onto the first description of follows: "There are three kinds of this sort of bronze: a Corinthian Bronze, quoted above, is a mention of white variety, coming very near to silver in brilliance, another bronze "valued in portrait statues and others in which the alloy of silver predominates; a second for its particular colour" which approached "the kind in which the yellow quality of gold predominates; appearance of liver and consequently called by a Greek and a third kind in which all the metals are blended in name hepatizon, meaning liverish." Pliny adds that "it equal proportions." (2). In another passage, Pliny notes is far behind the Corinthian blend" in value. As we the pleasing appearance that the gold and silver shall see, the reason why Pliny grouped this type of alloying elements lend to Corinthian Bronze (3). alloy together with Corinthian Bronze is that it also A story that circulated widely in the Roman contained gold and silver, although in much smaller Empire from the first century AD onwards related that proportions. Corinthian Bronze originated during the burning of Not surprisingly, it was the highly prized golden Corinth at the time of its capture by the Romans in variety of Corinthian Bronze that received most 146 BC (4). According to this account, the alloy was attention from ancient writers. The Jewish authors of first produced by accident when a building containing the Classical period were dazzled by the Corinthian gold, silver and much copper caught fire and the Bronze doors of the Nicanor Gate in the Temple in metals alloyed together (5). Jerusalem. These doors "far exceeded in value those From these descriptions, we learn that Corinthian doors plated in silver and set with gold" (7). The Bronze stood for a family of alloys containing gold and Nicanor Gate formed the main entrance to the inner silver, although we must presume that copper was the courts and was, doubtless, identical with the "Beautiful 60 §9' GoldBulletin2000,33(2) (yellow) and metal (gold) (15). The same manuscript also contains an abbreviated recipe for making "black Corinthian metal" (16). This would seem to refer to Pliny's dark-hued hepatizon bronze. Evidently, by the time that this text was composed, a blurring of the definition of Corinthian Bronze had occurred. Like Pliny's hepatizon, the black Corinthian metal is recommended in the Syriac text for use in statues. A later document, a lexicon composed in the l Oth century AD by the Syriac scholar Bar Bahlul, refers to Corinthian Bronze (17). Bar Bahlul agrees with Pliny that it is "part silver, part gold and part copper" and he adds that it is "bronze from which one makes gold and silver." This last statement finds an interesting echo in a recipe preserved in the Leiden Papyrus X, described Figure 1 Possible rep mentation ofthe GateofNicanor in the below. Temple in Jerusalem with itsgolden doors in a mural above the Torah shrineofthemid third centuryAD. synagogue ofDura Europos in Syria. CORINTHIAN BRONZE AND Gate" mentioned in Acts 3:2. According to the early DEPLETION GILDING Rabbinical work known as the Mishnah, this gate was the only one whose doors were not plated with gold, By scouring the ancient Greek, Latin and Syriac but composed of a bronze that shone "with a yellowish literature, it is possible to reconstruct the manufacture hue" (8). The Rabbinical authors agree explicitly with of Corinthian Bronze (18). We learn that its Josephus that these doors were made of Corinthian production involved further processing after alloying. Bronze, "which was as beautiful as gold" (9). Nicanor, This included a heat-treatment followed by a quench the donor of these precious doors, lived in the 1st and burnishing (19). All these constituent steps are century AD in Alexandria but was buried in Jerusalem, consistent with depletion gilding (or silvering), where his inscribed ossuary has been found (10). whereby copper is oxidized and removed from the According to the Jewish sources, the doors were surface of the bronze item by acid pickling, leaving the brought from Alexandria, his native city, and it is surface with a gold (or silver) layer, as explained below. reasonable to assume that they were also made there The alloying and processing technology suggested by (11). The Nicanor Gate is possibly the structure the sources for the production of Corinthian Bronze is depicted in fresco above the Torah shrine in the mid­ articulated in a recipe contained in the Leiden Papyrus X 2nd century synagogue at Dura Europos on the from Thebes in Egypt, the oldest surviving metallurgical Euphrates, which is preserved with the rest of the cycle text (20, 21). The papyrus appears to date from the of wall paintings in the Damascus Museum (12). The fourth century AD, but it has been shown that several of doors have two leaves, which are coloured yellow, to its recipes derive from even more ancient compilations represent gold (see Figure 1). (22). The relevant recipe (No. 15) describes a process Further association of Corinthian Bronze with a called "the colouration (chrJsis) ofgold": golden hue is to be found in Syriac sources. Thus, the "To colour gold, to render it fit for usage. Misy, salt Hebrew "goodly yellowed bronze" is rendered into and vinegar accruing from the purification of gold; Syriac as "Corinthian Bronze" in the Syriac "Peshitta" mix it all and throw in the vessel [which contains it] version of Ezra 8:27, datable to ca200 AD (13). Then, the [debased] gold described in the preceding in a Syriac text attributed to Zosim us, one of the early preparation; let it remain some time, [and then] having luminaries of alchemy, but composed between the 7th drawn [the gold] from the vessel, heat it upon the and l Oth centuries AD, a recipe is given "to make the coals; then again throw it in the vessel which contains golden or Corinthian colour" (14). Alongside this the above-mentioned preparation; do this several times heading in the surviving manuscript, preserved in until it becomes fit for use [ieas gold] (23). Cambridge, appears the symbol EB, which primarily From this description, we may discern a repeated represents the sun, but also the associated colour sequence of heat-treatment and pickling operations, ~ GoldBulletin2000,33(2) 61 using misy, salt and vinegar. Misy has been firmly identified with basic hydrated ferric sulphates, in (1) particular the mineral copiapite, which, when mixed Cas t i ngot with salt in solution, form ferric chloride and sulfuric acid (24,25). Ingot has duplex microstruct ure: (Cu + Au, Ag + Au phases) The manufacturing process in question would have corresponded to depletion gilding (or silvering), whereby the base metal, copper, is leached out of the surface of the alloy item by oxidation and acid pickling, to leave a gold- or silver-rich layer with a matt texture. A final burnishing operation is required to (2) achieve a bright finish. This is precisely the procedure Cold work and heat that was used by the pre-Columbian peoples of the in air Andes for manufacturing items of tumbaga (ie copper­ gold-silver alloys) (26 - 28). The probable recipe that was employed by the ancient American Indians for depletion gilding tumbaga has been reconstructed and Fe2(S04)3 + NaCI + H20 it is virtually identical to that given in the Leiden Papyrus X. The steps are as follows (29): (3) Porous Au 1) Cast an ingot of a copper alloy containing more than about 15wt% gold and approximately 5wt% Pickle silver. 2) Cold-work the ingot with intermediate annealing/quenching stages until the required ~ ~ D e n s e A u geometry is achieved. Although relatively hard, (4) such alloys have some workability when in an annealed condition. A black scale of cupric oxide Burnish forms on the surface.